Method of applying an organic coating onto an inorganic coated steel sheet for a magnetic laminate application

ABSTRACT

A continuous method is provided for improving the insulating characteristics of oriented steel strip having an inorganic surface coating to produce an organic resin-inorganic coatingoriented steel strip composite. Certain irradiation curable solventless organic resins can be continuously applied to the surface of the oriented steel strip in a pollution free manner. The resulting composite can be used to make power transformer core laminate.

United States Patent 1 Schroeter et a1.

1 1 METHOD OF APPLYING AN ORGANIC COATING ONTO AN INORGANIC COATED STEELSHEET FOR A MAGNETIC LAMINATE APPLICATION [75] Inventors: Siegfried I'I.Schroeter, Schenectady,

N.Y.; Jon Van Winkle, Dalton; Carroll B. French, Lenox, both of Mass.

[73] Assignee: General Electric Company,

Schenectady, NY.

{22] Filed: Feb. 22, 1974 [21] Appl. No.: 444,859

[52] US. Cl. 427/54; 204/159.15; 204/159.19; 336/219; 427/127; 427/403;427/409 [51] Int. Cl. B05D 3/06; HOlF 27/24 [581 Field of Search117/9331, 218, 219, 222, 117/215; 336/234, 219; 204/15915, 159.19;

[561 References Cited UNITED STATES PATENTS 2,354,123 7/1944 Horstman eta1. 148/6 1 1 Dec. 2, 1975 2,533,351 12/1950 Carpenter 148/635 3,531,3179/1970 Patheiger et 211..v 117/9331 3,600,290 8/1971 Fitko 117/93313,666,568 5/1972 Shimanaka et a1. 117/218 3,721,617 3/1973 Watt 117/93313,770,490 11/1973 Parker 1. 117/9331 Primary Examiner l. H. NewsomeAttorney, Agent, or Firm-William A. Teoli; Joseph T. Cohen; Jerome C.Squillaro [57] ABSTRACT 3 Claims, 2 Drawing Figures US. Patent Dec. 2,1975 FIG.

METHOD OF APPLYING AN ORGANIC COATING ONTO AN INORGANIC COATED STEELSHEET FOR A MAGNETIC LAMINATE APPLICATION The present invention relatesto the use of certain irradiation curable solventless organic resins forimparting improved insulating characteristics to oriented steel havingan inorganic insulating coating. More particularly, the presentinvention relates to a continuous, pollution free process for makingpower transformer core laminate.

Prior to the present invention, transformer core laminate was generallymade from oriented steel strip commonly referred to as magnetic orsilicon steel having an inorganic surface insulating coating such as amagnesium oxide or silicate, shown, for example, in Carpenter, et al.,U.S. Pat. Nos. 2,385,332 and 2,533,351, or having an inorganic phosphatecoated oriented steel as shown by Gifford U.S. Pat. Nos. 2,492,095 and2,501,846. etc. Further examples of inorganic coating materials forimparting improved insulating characteristics to magnetic sheet materialare shown by I-Iirst U.S. Pat. Nos. 3,562,011, 3,705,549 and 3,705,826,assigned to the same assignee as the present invention.

Although oriented steel processed by the abovedescribed methods providesuseful transformer core laminate, it was found that in many instancesthe inorganic coating did not insure adequate insulation. The inorganiccoating, for example, often had surface imperfections which causedvariations in surface resistivity, when oriented steel strip wassubjected to standard electrical and mechanical tests such as theFranklin test ASTM A344-68. Those skilled in the art also know that ifthe transformer core is not properly insulated, severe core damage canoccur in the event the transformer is struck by lightning. A highvoltage surge can result in permanent core insulation breakdown,resulting in higher core losses.

It has been found that improved insulating characteristics can beimparted to inorganic coated oriented steel strip by coating the steelstrip with an organic resin. An organic resin-inorganic coating-orientedsteel strip composite has been made by treating the oriented steel stripwith a hydrocarbon solvent solution of a phenol-formaldehyde resin.Although transformer core laminate having improved insulatingperformance can be made by use of such organic resin, the cure of theresin requires a baking step. Cure of the organic resin can require 1 to3 minutes, rendering the method undesirable for high-speed continuousoperation. In addition, means for hydrocarbon solvent removal must beprovided to avoid air pollution.

In addition to the requirement of insuring adequate insulation, thoseskilled in the power transformer art know that the core consisting ofhundreds of thin laminations in the form of high grade silicon steelstrips cut to size, must be immersed in C hydrocarbon oil. Oil immersionis required to improve heat transfer and to reduce corona around thecore and coils which could seriously damage and impair the operatingefficiency of the transformer. Experience has shown that the organicresin must be hydrolytically stable at temperatures up to about 100C fora period of about years in the hydrocarbon oil to satisfy manufacturingrequirements. Premature breakdown of the organic resin not only willresult in insulation failure of the transformer core, but

2 can also lead to the breakdown and reduction in the cffectiveness ofthe hydrocarbon oil to reduce corona.

A further criterion that a cured organic resin must possess before itwill meet the specifications of power transformer manufacturers is thatshrinkage upon cure will not have negative effects on properties. Thoseskilled in the transformer art know that shrinkage of certain coatingson the surface of the oriented steel strip can alter themagnetostriction characteristic of the steel. Even a slight increase inmagnetostriction due to surface stress can result in substantialtransformer hum.

The present invention is based on the discovery that certain solventlessirradiation curable organic resins, which are defined more particularlyhereinafter, and include both electron-beam curable and ultravioletlight curable resins, can be used to continuously make orientedsteel-inorganic coating organic resin composites in a pollution freemanner. The composites made in accordance with the practice of theinvention can be used as power transformer core laminates and areequivalent or superior in all respects to the core laminates made inaccordance with prior art procedures. This result is quite surprisingsince many available irradiation curable organic resins, such as shownby Patheiger et al., U.S. Pat. No. 3,531,317 cannot be employed toproduce suitable power transformer core laminate. In addition toimparting improved resistivity to inorganic material coated orientedsteel strip, one of the vital criteria required for operable solventlessirradiation curable resins in accordance with the practice of theinvention is hydrolytic stability or the ability to resist insulationbreakdown during immersion in 10C hydrocarbon oil over a 30-year periodunder average operating conditions of C. A further criterion employed isheat-stability. A weight loss test using a cured resin sample can beused to screen for heat stability whereby a weight loss of up to 10% canbe tolerated over a temperature range of to C over a 1,000 hour period.

A vital test for screening resins based on contamination of thetransformer oil and alteration of its dielectric properties is the IFTtest, ASTM D97l-50 Interfacial Tension of Oil Against Water, shown onpage 322 of the 1970 Annular Book of ASTM Standards, part 17 (November).It has been found that the IFT test can readily identify operablesolventless irradiation curable organic resins, which can be employed inthe practice of the invention. A procedure which can be employed is asfollows:

Four hundred fifty square inches of oriented steel strip having a 0.1mil cured coating of said irradiation curable solventless organic resinand capable of providing a O ampere Franklin test reading is immersed inabout 375 ml of 10C hydrocarbon oil which initially has about 9 39.0dynes/cm interfacial Tension Reading as measured above, and the 10Chydrocarbon oil is heated at a temperature of 120C for 48 hours. Inorder to qualify, the oil must provide thereafter an interfacial tensionreading of at least 30 dynes/cm.

A further surprising feature of the irradiation curable solventlessresins employed in the practice of the invention is that when applied tothe surface of oriented steel strip and cured in accordance with thepractice of the invention, there is little or no change in the dimensionof the strip sufficient to increase the magnetostriction of thetransformer core material made therefrom. A test procedure which can beused to determine strain of the oriented steel strip resulting from thecured resin is the Epstein test ASTM A343.

. There is provided by the present invention. a continuous.substantially pollution-free method for uniformly improving the surfaceresistivity of oriented steel strip having an inorganic material as asurface insulating coating to produce an oriented steel strip-inorganiccoating-organic resin composite capable of providing an average Franklintest reading of from 0.1 to amperes at a pressure of up to 300 psi,which comprises, l. treating the oriented steel strip with anirradiation curable solventless organic resin to a thickness of up to0.2 mil, and

2. passing the treated oriented steel strip through an irradiationcuring zone at a rate of from 100 to 600 feet per minute, using anirradiation flux sufficient to effect the cure of the solventlessorganic resin to an organic resin with a hardness capable of beingtested by the above-described Franklin test,

where said resin is characterized by having a viscosity of up to 3000centipoises at 25C, and is a mixture consisting essentially of from 99l%by weight of organic monomer and correspondingly from l-99% by weight oforganic polymer, where said irradiation curable solventless organicresin is capable of providing with C hydrocarbon oil, an interfacialtension reading of from 30 to 40 dynes/cm in accordance with ASTMD97l-501970).

Included by the irradiation curable solventless organic resins which canbe used in the practice of the invention are UV curable wax containingpolyesters as shown in copending application Ser. No. 444,860 ofSeigfried H. Schroeter and Ona Valys Orkin, filed concurrently herewithand assigned to the same 'assignee as the present invention. These UVcurable wax containing polyester can be more particularly defined assolventless organic-resins having a viscosity of from 500 centipoises to3000 centipoises containing the following essential ingredients byweight:

A. to 40% of a vinyl aromatic material selected from styrene, vinyltoluene,tert-butylstyrene and mixtures thereof,

B. 80 to 60% of an unsaturated polyester reaction product of (i) aglycol and (ii) and aliphatically unsaturated organic dicarboxylic acid,where i. is a glycol selected from the class consisting of a. a mixtureof 20-60 mole percent of neopentyl glycol and 40-80 mole percent of amember selected from propylene glycol, ethylene glycol and mixturesthereof, and

b. a mixture of (a) l to 40% by weight thereof of trimethylolpropanemonoallyl ether, and

ii. is an aliphatically unsaturated organic dicarboxylic acid consistingessentially of a mixture of 50 to 65 mole percent of fumaric acid and 35to 50 mole percent of a member selected from tetrahydrophthalicanhydride, endomethylene tetrahydrophthalic anhydride and mixturesthereof where there is utilized in making the unsaturated polyesterreaction product of (B), up to at least about l0 mole percent excess ofthe glycol of (i) over the aliphatically unsaturated organicdicarboxylic acid of (ii) C. 1% to 5% based on the weight of (A) and (B)of a UV sensitizer, and D. 0.05% to 1% based on the weight of (A), (B)and (C) of paraffin wax.

The above described unsaturated polyester can be made by standardtechniques involving either a onestep or two-step reaction procedure.The two-step procedure can involve reacting the total glycol attemperatures up to about 200C, which can consist ofa mixture ofpropylene glycol and neopentyl glycol, with tetrahydrophthalicanhydride. A hydrocarbon azeotroping solvent can be employed tofacilitate removal of Water of reaction. Upon allowing the reactionmixture to cool, an acid number of from I to 25 indicates completion ofthe first stage of the reaction. The fumaric acid can then be added tothe mixture with stirring and it is heated further until an acid numberof 5 to 15 is obtained. In the one stage cook procedure, the acid numbermay be as high as 30.

In preparing the UV curable polyester composition, the vinyl aromaticsolvent containing the paraffin wax and inhibitor can be added withstirring to the above prepared unsaturated polyester reaction productwhile it is warm. After the mixture has been allowed to cool to roomtemperature, an effective amount of the UV sensitizer can be added.

In addition to the above-described wax containing polyesters, there alsocan be used acrylic resins such as reaction products of acrylic ormethacrylic acid with bisphenol A diglycidyl ether, known for example,as Shell Epocryl 301, dissolved in styrene, vinyl toluene, hydroxypropylacrylate or hydroxypropyl methacrylate, or certain multifunctionalacrylates such as trimethylol propane triacrylate, etc. Other acrylicresins may be those derived from the reaction of hydroxyl terminatedpolyester glycols, etc. with diisocyanates and hydroxyl containingacrylates and methacrylates, or may contain randomly pendant acrylate ormethacrylate unsaturation. The cure of these resins is accomplished bythe free radical polymerization or copolymerization of said pendinggroups with those of the monomer molecules, the free radicals beinggenerated by the UV-activated sensitizer.

Another class of resins may include UV-curable epoxy resins, forexample, as described in US. Pat. Nos. 3,708,296; 3,721,6l6; and3,721,617. Such resins may consist of bisphenol A diglycidyl ethers suchas Epon Resins produced by Shell Chemical Co.; epoxidized phenol orcresol novolak resins such as produced by Dow Chemical Co. and CibaCorporation or blends of such epoxy resins with epoxide monomers such as1,2-epoxy-4( epoxyethyl) cyclohexane;( 3,4-epoxycyclohexyl)methyl3,4-epoxy cyclohexane carboxylate, allyl glycidyl ether, etc., ormixtures thereof. These epoxy resins may be cured by a cationicmechanism initiated by the UV-activated sensitizer.

Among the UV radiation photosensitizers which can be used in the curablewax containing polyester compositions of the invention are, for example,ketones, such as benzophenone, acetophenone, benzil, benzyl methylketone; benzoins and substituted benzoins such as benzoin methyl ether,a-hydroxymethyl benzoin isopropyl ether; halogen containing compoundssuch as abromoacetophenone. p-bromoacetophenone, ozchloromethylnaphthalene. sulfur compounds such as aromatic disulfides. and otherphotosensitizers such as azides, dyes. thioketones, or mixtures orsynergistic mixtures thereof. Other compounds, at levels which do notinterfere with the cure, may also be added. Such compounds are, forexample, inhibitors such as hydroquinone, tert-butyl hydroquinone,tert-butyl catechol, p-benzoquinone, 2.5-diphenylbenzoquinone,2,6-ditert-butyl-p-cresol, etc.; various fillers, flatting agents.thixotroptic agents. dyes and pigments such as barytes. blanc fixe.gypsum. calcium carbonate, quartz, diatomaceous silica, syntheticsilica, clay, talc. asbestine, mica, bentonite. aerogels, glass fibers,ultramarine blue, etc. In addition to the aforedescribed ingredients. upto 2% and preferably 0.05 to 0.3% of a wax. Suitable waxes include, forexample, low melting paraffin waxes having a melting point of about 40to 60C.

As shown in FIG. I of the drawing. a roller coater at 11 can be employedto continuously apply the irradiation curable organic resin onto theoriented steel strip at 10. The treated strip, in a preferred embodimentpasses through a UV curing zone 12 to effect the cure of the organicresin on the surface of the oriented steel strip. However. if desiredcure also can be effected by an electronbeam accelerator having anaccelerator voltage of from about 150 to 3,000 KV. The electrode currentshould as a rule have a strength between about 50 and 100 ma.

As indicated, cure of the organic resin is preferably effected by usingUV irradiation which can have a wavelength of from 1849 A to 4,000 A.The lamp systems used to generate such radiation can consist ofultraviolet lamps such as from 1 to 50 discharge lamps, for example,xenon, metallic halide, metallic are, such a low, medium or highpressure mercury vapor discharge lamp, etc., having an operatingpressure of from a few millitor to about atmospheres, etc., can beemployed. The lamps can include envelopes capable of transmitting lightof a wavelength of from about 1,849 A to 4,000 A, and preferably 2,400 Ato 4,000 A. The lamp envelope can consist of quartz, such as Spectrocilor Pyrex, etc. Typical lamps which can be employed for providingultraviolet radiation are, for example, medium pressure mercury arcs,such as the GE l-I3T7 arc, etc. The cures may be carried out with acombination of various lamps. some or all of which can operate in aninert atmosphere,

In operating the lamp to achieve a desirable level of flux intensityrequired for effecting cures of the solventless resin in a pollutionfree manner, the lamps can be ballasted to provide a higher watts perinch input than that normally rated by the manufacturer. For example,the GE H3T7 lamp normally operated at 130 watts per inch, can beoperated at up to 300 watts per inch input over a satisfactory operatinglife.

In addition to the above-described lamp means for generating ultravioletradiation employed in the practice of the invention as shown in FIG. 2,the means for providing such ultraviolet radiation in the apparatus usedtherein also may include radiation filtering means, such as quartzwindows at and 21, employed in combination with the lamp and reflectorto provide means for ultraviolet radiation having a wavelength of frombetween about 1,849 A to 4,000 A, while effecting the removal ofradiation greater than 7,500 A. The aforementioned windows can be madeof any suitable material capable of transmitting ultraviolet at awavelength of between 1,849 A to 4.000 A, such as quartz. Pyrex, Vycor,plastic sheets such as polymethylmethacrylate. etc. Typically, thefilters can be approximately the same size as the lamps or larger.

The thermal control means at 22 and 23 optionally can include supportmeans for the radiation filters, which when separated to a satisfactorydegree. such as 1 inch or more, can provide a channel. to allow for thepassage of air or water, to remove heat from the radia- 6 tion filters.Removal of heat also can be achieved by the employment of a cooling coilat 24 and 25 in instances where filter support means are employed.

The oriented steel strip which can be used in the practice of theinvention can include any electrical or magnetic steel suitable as acore material for power transformers or magnetic core structures formotors, generators and the like. Such steel can include silicon steelstrip having a thickness of 5 to 50 mil. preferably 11-25 mil, and awidth of 2 to in.

It has been found advantageous to coat the oriented steel with up to 0.2mil of resin and a rate of up to to 600 feet per minute.

When using UV lamps, the irradiation flux in the substrate can be atleast 0.01 watts per square inch to effectively cure the organic resinwithin 1 to 20 sec. and permit the steel strip to be taken up at a rateof from 100 to 600 feet per minutes. The strip can be cut to apredetermined width for use as transformer laminate.

In order that those skilled in the art will be better able to practicethe invention, the following examples are given by way of illustrationand not by way of limitation. All parts are by weight.

EXAMPLE 1 A polyester was prepared by initially stirring and refluxingunder nitrogen, a mixture of ingredients for about 4 hours at atemperature of up to about 200C. The mixture consisted of 0.50 mole oftetrahydrophthalic anhydride, 0.70 mole of propylene glycol, 0.40 moleof neopentyl glycol and 15 ml of toluene. At the termination of thereaction, the reaction product had an acid number of about 10. Thereaction product was allowed to cool to room temperature.

There was added to the above reaction product, 0.50 mole of fumaricacid, and the mixture was then heated and stirred to a temperature of upto 200C until a final acid number of about 10 was obtained. Volatileswere removed from the final product by blowing with nitrogen.

The above polyester reaction product was heated to C and there was added0.03 percent of hydroquinone. The polyester was allowed to cool to about1 10C and there was added with stirring a 0.2 percent styrene solutionof a paraffin wax having a m.p. of l33-135F. There was added sufficientstyrene to produce a composition having about 30 percent by weight ofstyrene. When the mixture cooled to room temperature, there was added asa UV sensitizer, about 3 percent by weight of the mixture of a blend ofiso-butyl and n-butyl ethers of benzoin. Based on method of preparation,the resulting mixture was a wax containing UV curable polyestercomposition. It had a viscosity of about 1,500 centipoises.

The viscosity of the resin at 24C measured with a Gardner BubbleViscosimeter, is Y to Z, corresponding to 18 to 23 stokes. Resinviscosity did not change over 3 months at room temperature. Themolecular weight of the resin was determined by gel permeationchromatography in methylene chloride against polystyrene with a 4 ft.column containing Pryrogel and Styrogel as support. The number averageweight found by this method was 2,500 i 500.

The above UV curable solventless polyester resin is then used to chargea roller coater as shown in the drawing. A roll of oriented siliconstrip steel. 24 inches wide and l 1 mil thick having a magnesiumsilicate inorganic surface coating is then coated on both sides with thepolyester resin to a thickness of about 0.1 mil and at a rate of from 10to 500 feet per minute. The treated strip is then passed through a UVcuring zone having several H3T7 lamps operated at 750 watts in air. Thelamps are spaced at a sufficient distance from the surface of the stripto provide at least 0.01 watts per in. light intensity.

During cure, there is generated less than 5% by weight of volatilesbased on the average weight of applied resin passing through the curingzone. The average exit temperature of the oriented steel strip substratedoes not exceed 150C. There is obtained an organic resin-inorganiccoating-oriented steel strip composite having a surface coating oforganic resin of about 0.1 mil.

A 2 X 8 inch strip is cut from the above composite and measured forsurface resistivity in accordance with ASTM A344 (Franklin'Test). It isfound that the strip gives an average reading of 0 to 001 amps at apressure of up to 300 psi. A 2 X 8 inch strip of the magnesium silicatecoated oriented silicon steel free of the polyester resin has an averagereading of 0 to 0.3 amps at the same pressure.

An interfacial tension test previously described is run in accordancewith ASTM D97l-50 with 450 in on the above polyester coated composite in10C hydrocarbon oil. A interfacial tension reading of at least 32 isobtained with the composite made in accordance with the practice of theinvention.

A similar interfacial tension test is made with a composite strip madefollowing the same procedure except that the polyester composition shownin the example of Patheiger et al., Pat. No. 3,531,317, is substitutedfor the UV curable polyester of the present. invention. There isobtained a reading of 23. As previously indicated, a reading of at leastis required.

In addition to passing the above described Franklin Tests and IFT test,the composites made in accordance with the practice of the invention aremeasured for magnetostrictio'n and magnetic properties at powerfrequencies. A magnetostriction change of A2 -0.1 is obtained on thecomposite tested at inductions of 15.5 kilogausses. A-c permeabilitychanges of composites at an induction of 10 orsteds are 0. There is nochange in core loss at 15.0 kilogausses after preparing the composites.

In addition to the above tests, a heat stability test in terms ofpercent weight loss is run at 150C over 1,000 hours with a 10 mil curedsample of the polyester resin of the present invention and the polyesterresin of Patheiger et al. The following results are obtained whereSchroeter signifies the polyester of the invention and Patheiger etalQis the prior art resin:

Percent Weight Loss Schroeter Patheiger. et al 1001) hrs. FranklinMugnctoat 150C.

(amps) ll-T striction (.2 wt. loss) phenolic 0 3H 0 l0 Schroeter 0 32-0.1 2

As previously indicated Schroeter represents a weight loss of less than5% volatiles during cure while phenolic can represent at least 65 /1.This dramatic reduction in weight loss percent of volatiles shows thesubstantially pollution free aspects of the method of the invention.

No loss of adhesion is observed when the composite film of the presentinvention is immersed in 100C water for 4 hours, boiling 5% KOH-solutionfor 30 min., or methylene chloride for 5 hours at room temperature.

EXAMPLE 2 The procedure of Example 1 is repeated except in place of theUV curable polyester resin, there is employed a UV curable acrylicresin. The aforesaid acrylic resin was prepared by effecting reactionbetween bisphenol A diglycidyl ether and acrylic acid employed in a l 2mole ratio in the presence of about 0.01 mole percent ofN,N-dimethylbenzylamine catalyst. A small amount of t-butyl catechol wasadded as a polymerization inhibitor. The reaction mixture was heated ina hot water bath at 90C with vigorous stirring. Periodically thereaction mixture was sampled and the acid number determined. When theacid number had fallen to 5 10, the reaction was terminated. The productwas stored in the dark. Four hundred fifty parts of the above acrylicresin was blended with 55 parts of trimethylolpropane triacrylatemonomer. To parts of the resulting blend, having a viscosity of 2,000centipoises, were added 0.3 parts of Michlers Ketone,4,4-Bis-(dimethylamino)benzophenone. During cure the temperature of theoriented steel strip is maintained below about 70C. There is obtainedless than about 5% by weight loss of volatiles. A 2 X 8 inch strip ofthe acrylic resin-magnesium silicate-oriented silicon steel compositeprovide the following values in the respective tests as shown in Example1.

Franklin 0.0 amps/1000 psi IFT 32 Heat Stability 8 wt. loss after 1000hrs. at C.

EXAMPLE 3 EXAMPLE 4 A 0.1 mil film of a polyester prepared from a resinof 0.6 mol of fumaric acid, 102 mol phthalic anhydride. 0.2 mol oftetrahydrophthalic anhydride, 0.6 mol neopentyl glycol and 0.4 molpropylene glycol having an acid number of is cut with styrene in a 60weight ratio. The resin is cured at a dose of 4.8 Mr at 80 ft/min in aninert nitrogen atmosphere to give a composite which shows an IFT of 32.

Although the above examples are limited to only a few of the very manyvariables which can be used in the method of the invention, it should beunderstood that the present invention is directed to the use of a muchbroader variety of UV curable resins, and to conditions used to effectthe cure of such resins on inorganic coated oriented silicon steel.

What we claimed as new and desire to secure by Letters Patent of theUnited States is:

l. A continuous, substantially pollution-free method for uniformlyimproving the surface resistivity of oriented steel strip having aninorganic material as a surface insulating coating to produce anoriented steel strip-inorganic coating-organic resin composite capableof providing an average Franklin test reading of from 0.1 to 0 amperesat a pressure of up to 300 psi, which comprises,

l. treating the oriented steel strip with an irradiation curablesolventless organic resin to a thickness of up to 0.2 mil, and

2. passing the treated oriented steel strip through an irradiationcuring zone at a rate of from 100 to 600 feet per minute, using anirradiation flux sufficient to effect the cure of the solventlessorganic resin to an organic resin hardness capable of being tested bythe above-described Franklin test,

LII

where said resin is characterized by having a viscosityof up to 3,000centipoises at 25C, and is a mixture consisting essentially of by weightfrom A. 20 to 40% of a vinyl aromatic material selected from styrene,vinyl toluene, tert-butylstyrene and mixtures thereof,

B. to 60% of an unsaturated polyester reaction product of (i) a glycoland (ii) an aliphatically unsaturated organic dicarboxylic acid, wherei. is a glycol selected from the class consisting of a. a mixture of20-60 mole percent of neopentyl glycol and 40-80 mole percent of amember selected from propylene glycol, ethylene glycol and mixturesthereof, and

b. a mixture of (a) l to 40% by weight thereof of trimethylolpropanemonoallyl ether, and

ii. is an aliphatically unsaturated organic dicarboxylic acid consistingessentially of a mixture of 50 to 65 mole percent of fumaric acid and 35to 50 mole percent of a member selected from tetrahydrophthalicanhydride, endomethylene tetrahydrophthalic anhydride and mixturesthereof where there is utilized in making the unsaturated polyesterreaction product of (B), up to at least about 10 mole percent excess ofthe glycol of (i) over the aliphatically unsaturated organicdicarboxylic acid of (ii) C. 1% to 5%- based on the weight of (A) and(B) of a UV sensitizer, and

D. 0.05% to 1% based on the weight of (A), (B) and (C) of paraffin wax.

2. A method in accordance with claim 1, where the inorganic coating onthe oriented steel strip is a magnesium oxide or a magnesium silicate.

3. A method in accordance with claim 1, where the cure of theirradiation curable resin is achieved with UV light having a wavelengthof from 1,849 A to 4,000 A.

1. A CONTINUOUS, SUBSTANTIALLY POLLUTION-FREE METHOD FOR UNIFORMLYIMPROVING THE SURFACE RESISTTIVITY OF ORIENTED STEEL STRIP HAVING ANINORGANIC MATERIAL AS A SURFACE INSULATING COATING TO PRODUCE ANORIENTED STEEL STRIP-INORGANIC COATING ORGANIC RESIN COMPOSITE CAPABLEOF PROVIDING AN AVERAGE FRANKLIN TEST READING OF FROM 0.1 TO 0 AMPERESAT A PRESSURE OF UP TO 300 PSI. WHICH COMPRISES,
 1. TREATING THEORIENTED STEEL STRIP WITH AN IRRADIATION CURABLE SOLVENTLESS ORGANICRESIN TO A THICKNESS OF UP TO 0.2 MIL, AND
 2. PASSING THE TREATEDORIENTED STEEL STRIP THROUGH AN IRRADIATION CURING ZONE AT A RATE OFFROM 100 TO 600 FEET PER MINUTE, USING AN IRRADIATION FLUX SUFFICIENT TOEFFECT THE CURE OF THE SOLVENTNESS ORGANIC RESIN TO AN ORGANIC RESINHARDNESS CAPABLE OF BEING TESTED BY THE ABOVE-DESCRIBED FRANKLIN TEST,WHRE SAID RESIN IS CHARACTERIZED BY HAVING A VISCOSITY OF UP TO 3,000CENTIPOISES AT 25*C, AND IS A MIXTURE CONSISTING ESSENTIALLY OF BYWEIGHT FROM A. 20 TO 40% OF A VINYL AROMATIC MATERIAL SELECTED FROMSTYRENE, VINYL TOLUENE, TERT-BUTYLSTYRENE AND MIXTURES THEREOF, B. 80 TO60% OF AN UNSATURATED POLYSTER REACTION PRODUCT OF (I) A GLYCOL AND (II)AN ALIPHATICALY UNSATURATED ORGANIC DICARBOXYLIC ACID, WHERE I. IS AGLYCOL SELECTED FROM THE CLASS CONSISTING OF A MIXTURE OF 20-60 MOLEPERCENT OF NEOPENTYL GLYCOL AND 40-80 MOLE PERCENT OF A MEMBER SELECTEDFROM PROPYLENE GLYCOL, ETHYLENE GLYCOL AND MIXTURES THEREOF, AND B. AMIXTURE OF (A) 1 TO 40% BY WEIGHT THEREOF OF TRIMETHYLOLPROPANE MONOALLYETHER, AND II. IS AN ALIPHATICALLY UNSATURATED ORGANIC DICARBOXYLIC ACIDCONSISTING ESSENTIALLY OF A MIXTURE OF 50 TO 65 MOLE PERCENT OF FUMARICACID AND 35 TO 50 MOLE PERCENT OF A MEMBER SELECTED FROMTETRAHYDROPHTHALIC ANHYDRIDE AND MIXENDOMETHYLENE TETRAHYDROPTHALICANHYDRIDE AND MIXTURES THEREOF WHERE THERE IS UTILIZED IN MAKING THEUNSATURATED POLYESTER REACTION PRODUCT OF (B), UP TO AT LEAST ABOUT 10MOLE PERCENT EXCESS OF THE GLYCOL OF (I) OVER THE ALIPHATICALLYUNSATURATED ORGANIC DICARBOXYLIC ACID OF (II) C. 1% TO 5% BASED ON THEWEIGHT OF (A) AND (B) OF A UV SENSITIZER, AND D. 0.05% TO 1% BASED ONTHE WEIGHT OF (A),(B) AND (C) OF PARAFFIN WAX.
 2. A method in accordancewith claim 1, where the inorganic coating on the oriented steel strip isa magnesium oxide or a magnesium silicate.
 2. passing the treatedoriented steel strip through an irradiation curing zone at a rate offrom 100 to 600 feet per minute, using an irradiation flux sufficient toeffect the cure of the solventless organic resin to an organic resinhardness capable of being tested by the above-described Franklin test,where said resin is characterized by having a viscosity of up to 3,000centipoises at 25*C, and is a mixture consisting essentially of byweight from A. 20 to 40% of a vinyl aromatic material selected fromstyrene, vinyl toluene, tert-butylstyrene and mixtures thereof, B. 80 to60% of an unsaturated polyester reaction product of (i) a glycol anD(ii) an aliphatically unsaturated organic dicarboxylic acid, where i. isa glycol selected from the class consisting of a. a mixture of 20-60mole percent of neopentyl glycol and 40-80 mole percent of a memberselected from propylene glycol, ethylene glycol and mixtures thereof,and b. a mixture of (a) 1 to 40% by weight thereof of trimethylolpropanemonoallyl ether, and ii. is an aliphatically unsaturated organicdicarboxylic acid consisting essentially of a mixture of 50 to 65 molepercent of fumaric acid and 35 to 50 mole percent of a member selectedfrom tetrahydrophthalic anhydride, endomethylene tetrahydrophthalicanhydride and mixtures thereof where there is utilized in making theunsaturated polyester reaction product of (B), up to at least about 10mole percent excess of the glycol of (i) over the aliphaticallyunsaturated organic dicarboxylic acid of (ii) C. 1% to 5% based on theweight of (A) and (B) of a UV sensitizer, and D. 0.05% to 1% based onthe weight of (A), (B) and (C) of paraffin wax.
 3. A method inaccordance with claim 1, where the cure of the irradiation curable resinis achieved with UV light having a wavelength of from 1,849 A to 4,000A.